Mig-21-Flight Model - Check six

Mig-21-FM-Identification-Rev. 14
Sustained load factor tables.
Once thrust and null-lift drag law have been approximated as described previously, the next step is to
determine Lift and Drag coefficient values for higher incidence values.
The aim of the analysis of the sustained load factor table is to define the Drag coefficient for incidence
values higher than the one deduced from level flight acceleration.
First of all, figures from the manual are analyzed in order translate them in tables giving the load
factor sustained (Extra Specific Power = 0) with full after burner for a given aircraft configuration, a
given altitude and a give mach number.
The aircraft configuration is assumed to be the same as previously: gross weight of 8,000 kg , drag
index of 12 (two IR missile).
For each value of Altitude, Mach number and load factor, the equation system describing the equality
of Lift and Apparent Weight on one side and Thrust and Drag on the other side has to be solved to find
the corresponding value of the Drag coefficient:
(6.1)
This simplified set of equation can be solved analytically, but it is its only advantage as it assume the
thrust force is applied along the speed vector, and this approximation can only be accepted only for
very small incidence angle (up to 5 degrees) that are not the one corresponding the flight conditions
such as the one described in “sustained load factor diagram” analyzed here.
So I chose to solve numerically the more precise equations set:
This allows the computation, for all points extracted from the figures to compute the value of the k
coefficient (defined by formula (5.1) here).
(6.4)
Page - 14